/*
 * Copyright 2002-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.reactive.result.condition;

import java.util.Collection;
import java.util.Collections;

import org.springframework.lang.Nullable;
import org.springframework.web.server.ServerWebExchange;

/**
 * A holder for a {@link RequestCondition} useful when the type of the request
 * condition is not known ahead of time, e.g. custom condition. Since this
 * class is also an implementation of {@code RequestCondition}, effectively it
 * decorates the held request condition and allows it to be combined and compared
 * with other request conditions in a type and null safe way.
 *
 * <p>When two {@code RequestConditionHolder} instances are combined or compared
 * with each other, it is expected the conditions they hold are of the same type.
 * If they are not, a {@link ClassCastException} is raised.
 *
 * @author Rossen Stoyanchev
 * @since 5.0
 */
public final class RequestConditionHolder extends AbstractRequestCondition<RequestConditionHolder> {

    @Nullable
    private final RequestCondition<Object> condition;


    /**
     * Create a new holder to wrap the given request condition.
     *
     * @param requestCondition the condition to hold (may be {@code null})
     */
    @SuppressWarnings("unchecked")
    public RequestConditionHolder(@Nullable RequestCondition<?> requestCondition) {
        this.condition = (RequestCondition<Object>) requestCondition;
    }


    /**
     * Return the held request condition, or {@code null} if not holding one.
     */
    @Nullable
    public RequestCondition<?> getCondition() {
        return this.condition;
    }

    @Override
    protected Collection<?> getContent() {
        return (this.condition != null ? Collections.singleton(this.condition) : Collections.emptyList());
    }

    @Override
    protected String getToStringInfix() {
        return " ";
    }

    /**
     * Combine the request conditions held by the two RequestConditionHolder
     * instances after making sure the conditions are of the same type.
     * Or if one holder is empty, the other holder is returned.
     */
    @Override
    public RequestConditionHolder combine(RequestConditionHolder other) {
        if (this.condition == null && other.condition == null) {
            return this;
        } else if (this.condition == null) {
            return other;
        } else if (other.condition == null) {
            return this;
        } else {
            assertEqualConditionTypes(this.condition, other.condition);
            RequestCondition<?> combined = (RequestCondition<?>) this.condition.combine(other.condition);
            return new RequestConditionHolder(combined);
        }
    }

    /**
     * Get the matching condition for the held request condition wrap it in a
     * new RequestConditionHolder instance. Or otherwise if this is an empty
     * holder, return the same holder instance.
     */
    @Override
    public RequestConditionHolder getMatchingCondition(ServerWebExchange exchange) {
        if (this.condition == null) {
            return this;
        }
        RequestCondition<?> match = (RequestCondition<?>) this.condition.getMatchingCondition(exchange);
        return (match != null ? new RequestConditionHolder(match) : null);
    }

    /**
     * Compare the request conditions held by the two RequestConditionHolder
     * instances after making sure the conditions are of the same type.
     * Or if one holder is empty, the other holder is preferred.
     */
    @Override
    public int compareTo(RequestConditionHolder other, ServerWebExchange exchange) {
        if (this.condition == null && other.condition == null) {
            return 0;
        } else if (this.condition == null) {
            return 1;
        } else if (other.condition == null) {
            return -1;
        } else {
            assertEqualConditionTypes(this.condition, other.condition);
            return this.condition.compareTo(other.condition, exchange);
        }
    }

    /**
     * Ensure the held request conditions are of the same type.
     */
    private void assertEqualConditionTypes(RequestCondition<?> cond1, RequestCondition<?> cond2) {
        Class<?> clazz = cond1.getClass();
        Class<?> otherClazz = cond2.getClass();
        if (!clazz.equals(otherClazz)) {
            throw new ClassCastException("Incompatible request conditions: " + clazz + " vs " + otherClazz);
        }
    }

}
